In a comparative study of cholate and deoxycholate, we examined the hepatic excretory transport characteristics of these bile salts, and compared their effects on biliary lipid and water output in bile fistula in rats. Our preliminary results indicated that over short courses of intravenous infusion hepatic excretory transport of either bile salt was fascilitated by the other. While the effects of each bile salt on cholesterol and water output into bile appeared similar, lecithin output with deoxycholate infusion was double that of the output with cholate infusion at similar rates. We also confirmed that hepatic lecithin excretion could not be increased at higher levels of cholate infusion. In the experiments for the coming year we will determine if this facilitation of hepatic excretion of one bile salt by infusion of another can be maintained over prolonged periods of infusion, and whether at infusion levels close to maximum excretory rates, any competitive inhibition can be demonstrated between cholate and deoxycholate. We will also examine the mechanisms which limit biliary lectithin output at higher levels of cholate excretion. Initially, we will infuse lecithin precursors to determine if it is the lack of lecithin availability in the liver which limits its excretion. Finally, the studies conducted thus far with cholate and deoxycholate will be extended to include chenodeoxycholic acid.